We have identified several growth factors and cytokines that can protect neurons against dysfunction and death in experimental models of Alzheimer's disease, Parkinson's disease and stroke. These trophic factors activate signaling pathways that stimulate the expression of genes whose encoded proteins increase resistance of neurons to oxidative and metabolic stress. Neuroprotective Actions of BDNF. We have found that brain-derived neurotrophic factor (BDNF) is a key mediator of the neuroprotective effects of dietary restriction in animal models of Parkinson's and Huntington's diseases. In other studies we have found that caloric restriction reduces damage to dopaminergic neurons and improves functional outcome in a non-human primate model of Parkinson's disease. The beneficial effect of CR is associated with increased amounts of BDNF and glial cell line-derived neurotrophic factor (GDNF), a growth factor which is now in early clinical trials in patients with Parkinson's disease. In related studies we have found that the antidepressant paroxetine can suppress neuronal degeneration and improve motor function and survival in a mouse model of Hungtington's disease by a mechanism involving increased production of BDNF. In addition, we have identified GLP-1 (glucagon-like peptide 1) as a neuroprotective neuropeptide with the potential to ameliorate neuronal dysfunction and degeneration in some neurodegenerative conditions. More recently, we have demonstrated a neuroprotective role for the mitochondrial uncoupling protein UCP4, which acts by reducing levels of oxidative stress. UCP4 expression increases in response to dietary restriction and BDNF treatment, suggesting a role for UCP4 in the neuroprotective effects of dietary restriction and neurotrophic factors. In preclinical studies we have developed novel analogs of uric acid and histidine as neuroprotective agents in a mouse model of stroke. We have also shown that intravenous immunoglobulin improves outcome following a stroke in mice, by a mechanism involving inhibition of the complement cascade.